Abstract: The choice of parting mode determines the difficulty of design in mold mechanisms such as the demolding mechanism and overall structure of the mold during the injection-molding process of a plastic part. Through combining with the shape characteristics of the plastic part for the bracket of B-mode ultrasound scanner, the design of the overall structure and demolding mechanism of the plastic part were simplified by choosing the parting surface of the plastic part reasonably. Aiming at the complexity of demolding process in the plastic part, a five?slider linkage mechanism was designed, in which the demolding of the inner wall with five buckles and the inner wall of concave part of the inner wall were implemented at first, then the demolding of the outer wall with two inclined guide-pillar slider mechanisms and core-pulling demolding of the side hole at the side end were performed, and finally the demolding of the plastic parts was completed by pushing the tube out. To meet the requirement for the action of the demolding mechanism, a three-plate mold holder was chosen. The first opening of the mold holder drove the core pulling action of the five-slider linkage mechanism, and the second opening drove the core pulling action of the side slider mechanism driven by the inclined guide pillar at the outer wall and side end. In the design of five-slider linkage mechanism, a central T?groove driving block was used to drive the intermediate transition slider, so that five forming sliders could be driven by dovetail groove connection to pull in core-pulling motion. Such a design artfully solved the problems in the inadequacy of design space for multi-core-pulling mechanism in the local area of plastic parts and ensured the reliability of automotive production for the injection molded plastic parts.